(1) Field of the Invention
The invention relates to a novel process flow for the formation of tapered contacts in boron and phosphorous doped tetraethyl orthosilicate, BPTEOS, films to achieve superior metal edge coverage when the contacts are filled with metal. The method uses a Buffered Oxide Etch, BOE, to remove a densified layer from the BPTEOS film followed by an isotropic etch and vertical anisotropic etch of the contact hole.
(2) Description of Related Art
Good metal step coverage is very important when filling contact or via holes in dielectrics with metal in the manufacture of integrated circuits. It is well recognized that tapered edges of the contact or via holes having a small entry angle, the angle between the surface of the dielectric film and the line tangent to the contact or via hole edge profile, is of critical importance in achieving good metal step coverage. U.S. Pat. No. 4,902,377 to Berglund et al., U.S. Pat. No. 5,164,340 to Chen et al., and Japanese Patent JA I-286442 to Ito teach methods for forming tapered contacts which. The method taught by this Invention uses process steps which differ from these. The method taught by this Invention provides a tapered contact or via hole with a small entry angle thereby achieving good edge coverage when the contact or via hole is filled with metal. The extra steps taught by this Invention to achieve a tapered contact or via hole do not appreciably reduce the throughput rate for contact or via hole formation.